Process for producing crimped polypropylene filaments

ABSTRACT

CRYSTALLINE POLYPROPYLENE HAVING AN INTRISIC VISCOSITY OF 1.2 TO 2.2 WHICH IS OBTAINED BY DEPOLYMERIZING POLYPROPYLENE HAVING AN INTRINSIC VISOCITY OF 1.2 TO 4.2 BY A DEPOLYMERIZATION DEGREE OF AT MOST 1.9 AND AT MOST 20% BY WEIGHT OF ADDITIVES IS MELT-SPUN THROUGH A SPINNERET AT A TEMPERATURE OF 260 TO 280*C. AND AT A SPINNING SPEED OF MORE THAN 600 M./MIN. TO FORM UNDRAWN FILIMENTS. THE RESULTANT UNDRAWN FILAMENTS HAVING AN INTRINSIC VISOCITY OF 0.8-1.4 ARE HEAT TREATED AT A TEMPERATURE OF 120-150*C., DRAWN AT A TEMPERATURE OF 110-150*C., AND THEREAFTER RELAXED TO PODUCE FINELY CRIMPED FILAMENTS HAVING A LARGE NUMBER OF CRIMPS AND GOOD CRIMP RETENTION ABILITY.

United States Patent Oflice 3,663,675 Patented May 16, 1972 3,663,675 PROCESS FOR PRODUCING CRIMPED POLYPROPYLENE FHLAMENTS Noboru Fukuma, Kenichi Matsui, and Hiroshi Shimizu, Nobeoka-shi, Japan, assignors to Asahi Kasei Kogyo Kabushiki Kaisha, Osaka, Japan No Drawing. Continuation-impart of application Ser. No.

869,450, Oct. 21, 1969, which is a continuation of application Ser. No. 706,674, Feb. 19, 1968. This application July 24, 1970, Ser. N 0. 58,207

Claims priority, application Japan, Feb. 28, 1967, 42/ 12,268 Int. Cl. D01d 5/22 US. Cl. 264-468 3 Claims ABSTRACT OF THE DISCLOSURE Crystalline polypropylene having an intrinsic viscosity of 1.2 to 2.2 which is obtained by depolymerizing polypropylene having an intrinsic viscosity of 1.2 to 4.2 by a depolymerization degree of at most 1.9 and at most 20% by weight of additives is melt-spun through a spinneret at a temperature of 260 to 280 C. and at a spinning speed of more than 600 m./min. to form undrawn filaments. The resultant undrawn filaments having an intrinsic viscosity of 0.8-1.4 are heat treated at a temperature of 120150 C., drawn at a temperature of 110l50 C., and thereafter relaxed to produce finely crimped filaments having a large number of crimps and good crimp retention ability.

This application is a continuation-in-part of Ser. No. 869,450 filed on Oct. 21, 1969, and now abandoned, which is a streamlined continuation of Ser. No. 706,674 filed on Feb. 19, 1968, which is now abandoned.

The present invention relates to an improvement in the process for manufacturing crimped polypropylene filaments. Various proposals, including a number of proprosals by the present inventors, have been made concerning methods of manufacturing crimped filaments from a composition comprising substantially crystalline polypropylene. As a result of further studies, the present inventors have developed an improved method for the production of crimped polypropylene filaments.

This invention relates to a process for producing crimped filaments, which comprises melt-spinning a corn position containing crystalline polypropylene having an intrinsic viscosity of 1.2 to 2.2 which is obtained by depolymerizing polypropylene having an intrinsic viscosity of 1.2 to 4.2 by a depolymerization degree of at most 1.9 and containing at most 20% by weight of additives through a spinneret heated to a temperature of 260 to 280 C., at a spinning speed of more than 600 m./min., to form undrawn filaments having an intrinsic viscosity (in tetralin at 135 C.) of 0.8 to 1.4, heat treating undrawn filaments at a temperature of 120 C. to 150 C. drawing the heat treated undrawn filaments at a draw ratio of 2.0 to 4.0 and temperature of 110 to 150 C., and relaxing said drawn filaments to form crimped filaments.

The crimped filaments of the invention have extremely fine crimps and have a crimping ability which remains substantially constant if the filaments are relaxed again, even if the filaments are kept under tension for a long time after drawing. Crimped filaments having very little give can be obtained by appropriate selection and regulation of the polypropylene starting material, the spinning conditions, the heat treatment of the undrawn filaments and the temperature at which the filaments are drawn. These conditions must all be maintained within limited ranges in order to obtain the advantages of the invention.

Crimped polypropylene filaments obtained by the practice of the present invention have a much larger crimping number and a far smaller crimping size in comparison with crimped polypropylene filaments which were previously known. If crimped polypropylene filaments obtained by previously known methods are kept under tension for a long time after the drawing process, for instance, if filaments are kept wound around the drawing pirn for several days, the crimping number decreases in comparison with the crimping number of filaments which are not kept under tension, and sufiicient crimps cannot be obtained even if the filaments are subjected to heat treatment after relaxation all of which results in a failure to obtain good marketable crimped filaments.

In contradistinction, even if the crimped filaments of the present invention are left for more than two days wound around the drawing pirn, the same extremely fine crimps as those obtained by relaxing immediately after drawing can be obtained within about two minutes. Moreover, even without heat treatment after storage, sufficiently fine crimps can be obtained, and the degree of fineness of the crimps changes little even if the filaments are subsequently heat treated.

The crystalline polypropylene starting material of the invention may be obtained by following generally known techniques for polymerizing polypropylene in the presence of an isotactic polypropylene producing catalyst. During the polymerization, partly noncrystalline polypropylene is produced as a by-product but this substance can be extracted by n-heptane or similar solvents. The present invention employs crystalline polypropylene having less than 20% and preferably less than 10% of a component which is extractable by n-heptane. The polypropylene raw material used for spinning must have a polymerization degree suitable for melt-spinning. For this purpose, crystalline polypropylene having an intrinsic viscosity of 1.2 to 2.2 which is obtained by depolymerizing polypropylene having an intrinsic viscosity of 1.2 to 4.2 is used. This polymer is melt and pushed out to form pellets for spinning. The polypropylene raw material of the present invention must also have a depolymerization degree of less than 1.9, preferably less than 1.5, to be suitable for the spinning operation. The term depolymerization degree is defined as follows:

Depolymerization degree= 1sp/C]P/['71 c]S In this formula, [1 p represents the reduced viscosity of the polymer obtained by the polymerization process, and 1s represents the reduced viscosity of the polymer when it is used as the raw material for spinning. As for the reduced viscosity this value is determined by measuring this viscosity of Tetralin solution of the polymer (0.1 g./ ml.) at C., with an improved model Ostwald viscometer.

If the depolymerization degree exceeds 2.0, suitable crimped filaments cannot be obtained even if the other requirements of the invention are carried out.

As additives to the polypropylene there may be employed various types of thermal stabilizers such as 2,6-ditert-butyl-p-cresol (0.1 weight percent), light stabilizers such as 2-hydroxy-4-octoxy-benzophenone (0.3 weight percent), stabilizers against gas discoloration, delustering agents such as titanium dioxide, fluorescent bleaching agents, pigments, crystalline nuclei forming agents such as sodium benzoate, and various types of dyeability accelerating agents, such as poly (aminotriazole) (520 weight percent) all of which additives are known in the prior art and have been used in making polypropylene filaments.

The conditions under which the polypropylene is melt spun are very important and must be carefully regulated. The spinning temperature should be 260-280 C. at the spinneret. If temperatures of as little as 10 C. higher or lower than this range are employed, fine crimps cannot be obtained even if the other steps of the process are carried out in accordance with the present disclosure. The spinneret temperature can be measured simply and accurately by making a small hole in the spinneret surface, and inserting a thermistor through the hole.

The spinning speed also influences the crimping characteristics of the resulting filaments. Although crimps can be obtained to some extent at a spinning speed of less than 600 m./min., it is necessary to have a spinning speed of more than 600 m./min. to obtain the fine crimps sought by the present inventors.

The intrinsic viscosity of the pellets before spinning used in the present invention must be 1.2-2.2, but the intrinsic viscosity of the taken-up undrawn filaments thus spun should be 0.8-1.4 to give excellent crimpable filaments. The intrinsic viscosity of 0.8-1.4 of the undrawn filaments should be given by just the way by which the pellets are extruded and melt-spun under the conditions as described above. In another words, the intrinsic viscosity of the undrawn filaments ranging from 0.8 to 1.4 may be resulted by from carrying out process under only the conditions that:

(a) making pellets of crystalline polypropylene having an intrinsic viscosity of 1.2 to 2.2 which is obtained by the depolymerization of polypropylene having an intrinsic viscosity of 1.2 to 4.2, and melting and extruding the pellets having intrinsic viscosity of 1.2 to 2.2,

(b) depolymerizing the pellet to a depolymerization degree of 1.9 or less;

(c) keeping the temperature of the spinneret at 260- (d) spinning the melted polymer through a spinneret at a speed of 600 m./min. or more.

Comparison in crimping effect was made between the undrawn filaments obtained by the process of the present invention and other filaments as follows:

Experiment number 1 2 3 Intrinsic viscosity of pellets 2. 1 2. 1 2. 1 Depoly-merization degree of pellets. 1. 3 1. 3 1. 3 Spi'nneret temperature, C 245 275 295 Take-up speed, m./miu 800 800 800 Heat-treatments of resulted undrawn filaments, 120 120 120 with steam, C. Time of said heat-treatment, min 30 30 3O Intrinsic viscosity of the undrawn filaments 1. 6 1. 3 1. Number of crimps 8 23 Within the scope of this invention No Yes No As is apparent from the above table, only when both the temperature of the spinneret and the intrinsic viscosity of the obtained undrawn filaments are satisfactory for the range of the present invention, are the crimped filaments produced in satisfactory state. If the intrinsic viscosity of the undrawn filaments is over 1.4, crimpability is extremely bad, and moreover, if the filaments consist of such fine filaments as have less than 3 denier for each single filament, there occur so many breaks of the single filament during the spinning or so much denier unevenness appears that the filaments are not suitable for commercial use. On the contrary, if the intrinsic viscosity is less than 0.8, it is hard to obtain crimped filaments for use.

It is also necessary that the conditions under which the undrawn filaments are heat treated, and the drawing conditions be carefully regulated. If the heat treatment of the undrawn filaments is either omitted or carried out at a temperature lower than the prescribed range of 120- 150 C., either no crimps are obtained, or the crimps are far inferior to the fine crimps which are the object of the present invention, even if drawing is carried out in the prescribed range of -150 C., and the filaments are thereafter relaxed. The heat treatment of the undrawn filaments within the prescribed temperature range apparently has the effect of increasing the potential crimp producing ability of the filaments, as is seen from the fact that crimps can be obtained even if drawing is done at a temperature of 1l0-150 C., although it has heretofore been considered that crimps could not be obtained at such high drawing temperatures. Furthermore, according to the invention, finer crimps can be obtained than those obtainable by drawing at lower temperature filaments which were not subjected to the heat treatment.

The temperature and the duration of the heat treatment are inversely related, i.e., to achieve the same effect of the heat treatment step, at high temperatures, the duration of the heat treatment may be shorter. For instance, at a temperature of 130 C., a duration of about 30 minutes for the heat treating step will do, but at a temperature of C., more than one hour is required. The duration of the heat treatment will normally vary from about 10 minutes to about 2 hours.

Referring to the drawing step, if an attempt is made to draw the heat treated filaments described above at a temperature lower than the prescribed temperature range of 110-150 0., either drawing is impossible or only a low draw ratio is possible. A low draw ratio is not acceptable since this results in insufiicient crimps in the filaments, and crimped filaments having fine crimps which are the object of the present invention cannot be obtained at low draw ratios.

When drawing is done at the prescribed temperature, the draw ratio is not specifically limited but it is normally 1.1-5.0, preferably 2.0-4.0.

When the filaments are stretched at a temperature within the prescribed temperature range, not only is crimping possible, but it was found that extremely fine crimps which had heretofore been impossible to obtain by conventional methods were obtained without subsequent heat treatment, with the result that fine crimped filaments were obtained with a crimp producing ability which was not lowered even if the filaments were left to stand under tension for a long time. The moment that the drawn filaments were relaxed, crimps were produced so that heat treatment after relaxation is not necessarily required in the process of the present invention.

The number of crimps differs according to the denier of the filament. Fine crimps can be obtained according to the present invention with a number of crimps of more than 40 per 25 mm. in the case of single 1-5 (1. filament for clothing, and 25 per 25 mm. even in the case of single 15 d. filament. The number of crimps according to the commonly known process is less than a half of that which can be obtained according to the present invention.

If the filaments are relaxed immediately after drawing, extremely fine crimps are produced almost immediately. On the other hand, if the filaments are left wound around the pirn for more than two days, the drawn filaments nevertheless almost reach an equilibrium status within two minutes after relaxation. Moreover, the same fine crimps are obtained as those achieved by relaxing the filaments immediately after stretching. The crimps which reached equilibrium at room temperature exhibit little change even if subsequently heat treated, i.e., subsequent heat treatment and relaxation aimed at producing crimps are not required. However, such treatment and relaxation may be done for the purpose of shortening the time for reaching equilibrium or for further stabilizing the obtained crimps.

Since the crimped filaments of the invention have the properties mentioned above, if the drawn filaments are subjected to a knitting process directly from a drawing pirn, the crimp producing speed is fast and crimps can be produced under the tension applied to the filaments at the time of knitting, so that a product similar to knitted goods obtained by knitting ordinary crimped yarns produced by conventional methods can be obtained,

It will be appreciated that these new methods, which have heretofore not been considered possible are attributable to the unprecedented and unique properties of the (1) While Benson doesnt prescribe the depolymerization degree, the present invention requires that the depolymerization degree should be less than 1.9.

(2) There is a difference in the intrinsic lviscosity of the pellets before spinning: In Benson it is 1.0-6.0 and in the examples of Benson materials whose viscosity is as high as 3.2 are necessary, while that of the present invention is 1.2-2'2.

(3) A difference in the intrinisic viscosity of the drawn filaments obtained: In Benson the viscosity is as high as 1.5-2.5, while in the present invention it is 0.8-1.4.

(4) Other differences are found in the regulation of spinning speed and in the process for heat-treatment of undrawn filaments.

"In addition to the above stated apparent dilferences, according to Benson no filament of fine denier can be obtained and even in the examples the single yarn denier is as thick as 15-27 denier. Furthermore the number of crimps is extraordinaly few and rough in Benson. The last few ditferences of the above from the present invention will be stated in the following examples.

The terms crimp extension percentage and the crimp recovering percentage, which are used in the following examples to show the crimping characteristics of the crimped filaments obtained according to the present invention, are defined as follows:

LS o

Crimp extension percentage= X 100 (percent) X100 (percent) Crimp recovering percentage= Note The present invention is further described in the following examples.

EXAMPLE 1 With titanium trichloride and diethyl aluminum chloride used as catalysts and a small amount of hydrogen as a molecular weight modifier, propylene was polymerized in n-hexane, and the resultant polymer was refined to obtain polypropylene in powdery form having a reduced viscosity of 2.0, i.e., an intrinsic viscosity of 1.8, and nheptane content of 2.1%.

As a thermal stabilizer, 0.1% of 2,6-di-tert-butyl-pcresol was added to this polymer, and this mixture was treated in a pelletizer to obtain a granular polymer having a reduced viscosity of 1.8, i.e., an intrinsic viscosity of 1.65, for use as a spinning raw material. The depolymerization degree of this raw material was 1.1.

For spinning, an ordinary type of melt spinning machine comprising a combination of an extruder and a gear-pump was used. The temperature at the spinneret was 265 C. The spinneret had 24 holes, each having a diameter of 0.45 mm. The extruded melt filament was cooled down by cold air having a temperature of 20 C. The spinning was carried out at atake-up speed of 800 m./min.

The resultant undrawn filaments were treated for one hour at 140 C., as they were wound around bobbins. These undrawn filaments were drawn by a conventional draw twister. Drawn filaments of 70 d./24 filaments were obtained under the following drawing conditions, i.e., a drawing temperature of 140 C., a draw ratio of 3.0, and a drawing speed of 400 m./min.

Within 30 minutes, the resultant drawn filaments were made into a hank form, with the result that extremely fine crimps were produced, and they quickly reached an equilibrated status. The characteristics of the crimped filaments were as follows:

Intrinsic viscosity-1.2

Crimp extension percentagel 20% Crimp recovering percentage-91% Number of crimpsS 1/25 mm.

These hanks, after being treated for 30 minutes by steam at C., exhibit little differences from those which were not subjected to said treatment having the following properties:

Crimp extension percentage-l 25 Crimp recovering percentage-93% Number of crimps-5 l 25 mm.

EXAMPLE 2 Undrawn filaments produced as in Example 1 were left wound around the drawing pirn for a week in a room at 20 C., and thereafter were made into a hank form. Two minutes after the hank was taken out of the hank frame, the crimps reached equilibrium, and crimped filaments having the followin characteristics were obtained:

Intrinsic viscosity1.2

Crimp extension percentage120% Crimp recovering percentage92% Number of crimps49/25 mm.

As a result of treating these hanks with steam at 120 C. for 30 minutes, they were converted into crimped filaments having the following characteristics:

Intrinsic viscosityl .2

Crimp extension percentage-120% Crimp recovering percentage-93% Number of crimpsS l/ 25 mm.

EXAMPLE 3 To crystalline polypropylene of powdery form having a reduced viscosity of 2.5 i.e., an intrinsic viscosity of 2.2 obtained through polymerization by the same method as in Example 1, there was added 0.2% of 2,6-di-tert-butyl-pcresol as a thermal stabilizer. This mixture was extruded from a pelletizer in granular form, and a polymer having a reduced viscosity of 2.0, i.e., an intrinsic viscosity of 1.8 was obtained. This polymer was used as a raw material for spinning. The depolymerization degree of this polymer was 1.25. The undrawn filaments obtained by spinning this polymer through a spinneret at a temperature of 275 C. and a spinning speed at 1,000 m./min., were subjected to heat treatment at C. for 30 minutes. The heat treated filaments were drawn at a ratio of 3.0 at C., to obtain drawn filaments of single 15 d. filament. When these filaments were made into hank form within 30 minutes after drawing, an equilibrium condition was quickly reached, and crimped filaments having the following crimping characteristics were obtained:

Intrinsic viscosity-l .3

Crimp extension percentage90% Crimp recovering percentage92% Number of crimps--35/25 mm.

7 Also, when the stretched filaments were left to stand at room temperature for a week while wound around the stretching pirn, the crimping condition reached an equilibrium in about 2 minutes, and the following characteristics were obtained:

Crimping elongation80% Crimping magnification-88% Number of crimps30/ 25 mm.

When these filaments were treated with steam at 120 C., the crimping characteristics became as follows:

Crimping elongation-83 Crimping magnification90% Number of crimps-32/ 25 mm.

EXAMPLE 4 3 kg. of trioctylamiue and 3 kg. of precipitated calcium carbonate having a mean granular diameter of 005g were mixed with 94 kg. of granular polypropylene having an intrinsic viscosity of 1.8 and a depolymerization degree of 1.25 which was obtained by the same method as in Example 3. This mixture was extruded from a pelletizer to obtain a granular polymer. This polymer was subjected to spinning through a spinneret at a temperature set at 265 C. and spinning speed at 900 m./rnin. The resultant filaments were heat treated at 135 C. for 20 minutes.

The resultant heat treated undrawn filaments were drawn to 2.3 times at 140 C. to obtain drawn filaments of 100 d./24 f. These drawn filaments were made into a hank form within 30 minutes after drawing. As a result, extremely fine crimps were obtained, with an equilibrium reached within 1 minute. The characteristics of the crimped filaments were as follows:

Intrinsic viscosity1.3

Crimp extension percentage-115% Crimp recovering percentage90% Number of crimps-48/25 mm.

By treating these filaments with steam at 120 C. for 30 minutes, crimped filaments having the following characteristics were obtained:

Crimp extension percentage120% Crimp recovering percentage-92% Number of crimps-SW25 mm.

These crimped filaments after treating were subjected to dyeing in a hank form under the following conditions:

DyestuffC.I. Acid Orange 7, 15510, 3% O.W.F. Liquor ratio1:50

AuxiliarySalicyclic acid 4 g./l.

Dyeing temperature-98 C.

Dyeing time60 min.

As a result, the filaments were dyed a reddish orange. The characteristics of the resultant crimped filaments were the same as those before dyeing and no yielding was recognized. (This is an example in which the draw ratio was 2.3 times.)

EXAMPLE 5 Spinning material was prepared by mixing the same crystalline polypropylene as used in Example 1 with 5% of titanium dioxide. The spinning conditions are as follows:

Temperature of molten polymer280 C. Temperature of spinneret-268 C. Spinning speed-1000 m./min.

Diameter of each hole0.45 mm. Number of holes in spinneret-24 The thus obtained undrawn filament of 300 d./ 24 f. was treated with steam at 120 C. for 30 minutes and thereafter it was stretched with a stretching ratio of 3.0 at 130 C. which was the temperature of the hot-plate. The

8 thus stretched filament was kept for two days in a room at 25 C. and then wound up in the shape of a pirn. Through this process one obtained crimped filament whose nature was as follows:

Crimp extension percentage% Crimp recovery percentage-88% Number of crimp47/25 mm. Intrinsic viscosity1.2

On the other hand, when a pirn-shaped filament was obtained through the same process except that the spinning speed was 400 m./min., the number of crimp was as few as 8/25 mm. All that could be obtained by the method as above was a very poor filament, i.e., poorly crimped filament. The intrinsic viscosity was 0.8.

EXAMPLE 6 To the same polypropylene granules as employed in Example 3 was added 6% by weight of Nylon 6 polymer, 3% by weight of precipitated calcium carbonate having a mean granular diameter of 0.05p. and 8% of liquid paraffin, and the combined materials were mixed well by using a Banbury mixer and then re-pelletized by means of an extruder.

Employing the thus prepared raw material the same procedures as described in Example 1 were repeated except for the following conditions:

Spinning step:

Temperature of molten polymer-270 C. Temperature of spinneret--255 C. Spinning speed-800 m./min.

The resultant undrawn filaments were treated for one hour at 140 C. as they were wound around bobbins. Drawn filaments of 70 d./24 filaments were obtained under the following drawing conditions, i.e., a drawing temperature of C., a draw ratio of 3.0, and a drawing speed 300 m./rnin.

Within 1 hour, the resultant drawn filaments were made into a hank form, with the result that extremely fine crimps were produced, and they quickly reached an equilibrium state.

The characteristics of the crimped filaments were as follows:

Crimp extension percentage145% Crimp recovering percentage85% Number of crimps-41/25 mm. Intrinsic viscosity-1.1

When the crimped filaments were dyed with an acid dye, CsI. Acid Red 85, 22245, with salicylic acid (concentration 4 g./l.; liquor ratio 50 times) as an auxiliary, deep red colored products were obtained.

Comparison 1 Isotactic polypropylene having an intrinsic viscosity (in Tetralin at C.) of 3.3 to which 0.4% of an antioxidant and 0.02% of di-butyl tin maleate as a thermal decomposer was fed into a 25 mm. screw-extruder from which the molten polymer was supplied to a metering pump and thence through a filter consisting of 10-20 mesh sand to a two hole spinneret (hole diameter: 0.015 inch). These spinning conditions are shown in Table l. The spun yarns were then cold drawn using a water bath at 90 C. at the required draw ratio and at a draw speed of 200 feet per minute. The drawn yarns were then relaxed quickly by cutting the yarn off the draw bobbin and stabilized by heating in air at C. for twenty minutes. The Table 1 which follows shows the effect of spinning temperature and wind-up speed on the intrinsic viscosity and birefringence of the spun yarn and the effect of draw ratio on the degree of spontaneous crimping obtained.

The information obtained from these spinning tests is as follows.

(1) Since a high molecular weight pellet was spun while being decomposed, the variation in pressure in the spinning machine was large and the filament obtained was not stable. (Unevenness of denier was found to be as much as 4%.)

(2) A spiral movement was caused at the spinneret face and the state thereof was varied with the lapse of time.

(3) The resultant crimped filament was conspicuously low in degree of crimping as compared with the crimped filament obtained in accordance with the present process. Further, there was unevenness in the degree of crimping of the resultant filament and it may be said that the resultant crimped filament had entirely no commercial value.

(4) The finely crimped filament obtainable in accordance with the present invention could not be obtained unless the wind-up speed was 1800 ft./min. or more, while the filament of Benson could be obtained even in the wind-up speed of 1000 ft./min.

(5) The extruded filament obtained at a spinning temperature of 250 C. or less was in a state of slub and there occurred break of single filament and then it was hard to be taken up.

Comparison 2 Extrusions were eifected through a spinneret of 0.015 inch x 2 holes at a spinning temperature of 260 C. and taking-up velocity of 2000 lit/min. varying the extruding amount with the use of the same pellet and device as in Comparison 1. The taken-up filament was immediately heat treated at 140 C. for 30 minutes without drawing. The results are shown in Table 2.

10 The information obtained by these spinning tests is as follows.

(1) A single filament of 10 d. was often cut during spinning. A single filament of 5 d. could not be taken up.

(2) The degree of crimping the resultant filament was conspicuously low as compared with that of the crimped filament of the present invention.

(3) The present crimped filament is readily taken up even in 2 d. Bensons filament becomes impossible to be spun, since the degree of polymerization of the pellet is toohigh.

What is claimed is:

1. A process for producing crimped polypropylene filaments, said process comprising melt-spinning crystalline polypropylene having an intrinsic viscosity of 1.2 to 2.2 which is obtained by depolymerizing polypropylene having an intrinsic viscosity of 1.2 to 4.2 by a depolymerization degree of less than 1.9, and at most 20% by weight of additives through a spinneret heated to a temperature of 260 to 280 C., at a spinning speed of more than 600 m./min. to form undrawn filaments having an intrinsic viscosity of 0.8 to 1.4, heat treating the undrawn filaments at a temperature of to C., drawing the heat treated undrawn filaments at a draw ratio of 2.0 to 4.0 and a temperature of 110 to 150 C., and relaxing said drawn filaments to form crimped filaments.

2. A process according to claim 1, wherein the crystalline polypropylene to be spun has an intrinsic viscosity of 1.2 to 2.2.

' 3. A process according to claim 1, wherein heat treating is carried out for 10-120 minutes.

References Cited UNITED STATES PATENTS 2,947,598 8/1960 Maragliano et a1. 264-210 F 3,013,003 12/1961 Maragliano et a1. 264-210 F 3,093,444 6/1963 Martin 264-210 F 3,137,989 6/1964 =Fior et al 57-140 3,143,584 8/1964 Roberts et a1 2154-210 F 3,215,486 11/1965 Hada et al. 8-74 3,233,023 2/1966 Benson 264-168 3,256,258 6/1966 Herrman 26 0-937 3,323,190 6/ 1967 Boltniew 264-210 F 3,432,590 3/1969 Papps 2-64-210 F 3,560,604 2/ 1971 Papps 264-210 F FOREIGN PATENTS 20,770 12/1966 Japan 264-176 F JAY H. WOO, Primary Examiner US. Cl. X.R. 

